Copper deposits typically have copper-bearing zones at different depths that contain different copper-bearing minerals. Copper oxides, such as malachite and chrysocolla, are located in an upper weathered zone. A mixture of copper sulfides, such as chalcocite, covellite, and chalcopyrite and copper oxides are generally located below the upper weathered zone in an intermediate enriched zone. Chalcopyrite is generally located in a primary mineralized zone below the intermediate enriched zone.
The copper in the ores from the various zones is recovered by different techniques. The copper in the ore from the upper weathered and intermediate enriched zones is typically recovered by heap leaching techniques. Because it is difficult to economically recover the copper in the chalcopyrite located in the primary mineralized zone by heap leaching techniques, copper in ore from the primary mineralized zone is recovered by other techniques.
Smelting and refining is the traditional approach used to recover the copper in the ore from the primary mineralized zone. Because the smelting and refining process is expensive, the copper sulfides in the ore are first concentrated into a copper sulfide concentrate by flotation techniques to provide a smaller volume of material for smelting. The sulfide concentrate is then shipped to a smelter/refiner which heats the concentrate to high temperatures to form a crude copper product which is refined to a highly pure metal. In recent years, the smelting and refining process has fallen into disfavor due to environmental problems associated with the disposal of smelting and refining byproducts and increases in smelting and refining costs.
A process developed as an alternative to smelting and refining is to slurry the copper sulfide concentrate and oxidize the sulfur in the copper sulfides to sulfuric acid and the copper to copper sulfate under conditions of high temperature and superatmospheric pressure to form a copper-containing solution. The copper is recovered from the solution by solvent extraction and electrowinning techniques to provide a cathode copper product of high purity at the mine site. Because a high acid concentration is undesirable in solvent extraction due to unfavorable equilibrium conditions, the leach solution is neutralized before solvent extraction and electrowinning using lime or an acid-consuming, low-grade copper ore. Unlike the smelting and refining process, this process does not generate harmful offgases and other harmful byproducts and is therefore more environmentally safe than smelting and refining.
Although the process is more environmentally safe than smelting and refining, this process has unacceptably high copper losses. The use of lime to neutralize the acid in the solution not only increases operating costs due to lime consumption but also forms a low pulp density slurry from which it is difficult to recover the copper. Alternatively, the percolation of the solution through a heap of an acid-consuming, low-grade copper ore to neutralize the acid in the solution can cause copper losses in the heap.
There is a need for a low-cost method to recover copper from copper-containing sulfides, especially copper from copper sulfides such as chalcopyrite, that has a high copper recovery rate.